A variety of transportation facilities, involving automobiles, have seats equipped with seat belt devices for protecting vehicle occupants from injuries during emergencies such as collisions. In order for the seat belt device of this kind to be simply buckled or unbuckled, the seat belt device normally includes a buckle device in which in general, a latch member for latching a tongue plate is spring urged toward the tongue plate in a latch direction and a lock member allows the latch member to keep the tongue plate and the buckle body under a latched status.
By the way, with such a buckle device, a need arises for a lamp to provide a display of the presence of the tongue plate and the buckle body remaining under the latched status, for a belt winding force reduction mechanism of a retractor or the like to be controllably operated, or for buckling and unbuckling information of the seat belt to be transmitted to an air bag ECU (electronic Control Unit). To this end, the buckle body internally has a buckle switch for detecting the latched status.
A prior art related to the buckle switch of this kind includes, for instance, a Patent Literature 1 described below.
FIG. 8 is an illustrative view related to a buckle device disclosed in the Patent Literature 1.
With a structure shown in FIG. 8, as a tongue plate 111 is inserted from a non-latched status into a buckle body 140, a distal end 123d of a latch member 123, disposed inside the buckle body 140, is latched to a latch hole 112 formed in a distal end of the tongue plate 111.
Disposed inside the buckle body 140 are a first switch section 133, composed of a hall element 131 and a permanent magnet 132, and a second switch section 151 operative to perform switchover between an NC (Normally Closed) contact and an NO (Normally Open) contact. With the first switch section 133, a first section of the magnet 132 is placed in face-to-face relationship with the hall element 131 during a non-latched status and a second section of the magnet 132 is placed in face-to-face relationship with the hall element 131 during a latched status, thereby making it possible to detect whether the tongue plate 111 and the buckle body 140 remains under the latched status or non-latched status.
An unbelted warning lamp (not shown) is connected to the NC contact of the second switch section 151 and an electromagnetic solenoid (not shown) of a winding force reduction mechanism is connected to the NO contact. For instance, as an occupant starts up an automobile, an ignition switch IG is turned on at which time under the non-latched status, the unbelted warning lamp is lighted up and upon the occurrence of the latched status, the electromagnetic solenoid is energized to render the winding force reduction mechanism operative for thereby alleviating a clamping force of a webbing by which the occupant is restrained. Further, the ECU detects the magnitude of electric current flowing through the hall element 131 of the first switch section 133 and if the tongue plate 111 and the buckle body 140 remain under the latched state, then, an airbag is rendered operative or the magnitude of an airbag output can be altered.    Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2003-81057